Fix null ref exception when trying to start the timer.
Use LINQ First instead of indexed accessor.
BeginUpdates before swapping cache.

In some edge-case the UITableView might call some of the overrided
methods after we've swapped the cache and before we are in updating
mode. So need to swap the cache only after we've told UITableView that
were about to be updated.
Fix formating.
Catch InvalidOperation exceptions and log them.
Merge pull request #267 from toggl/roosmaa-bugsnag-fixes

Various small bugfixes.